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Sunyaev-Zeldovich Universe and the Future of Cluster Cosmology

Conference Date:

Monday, April 27, 2009 (All day) to Friday, May 1, 2009 (All day)

Galaxy clusters have played a crucial role in the development of modern cosmology over the past century. Thanks to the next generation of high resolution microwave telescopes, a new generation of cluster surveys (detected through the Sunyaev-Zel'dovich (SZ) effect) are under way and promise to provide us with a catalog of hundreds to thousands of new high redshift clusters over the next few years. This conference aims to bring together experts in SZ observations and cluster cosmology to understand the status/implications of current clusters surveys, and find a consensus on the future promise/prospects of cosmology with galaxy clusters.

The observed thermal properties of the ICM shows much greater dispersion than expected if the gas was subject only to shock-heating by mergers and during infall. This diversity can be best understood as a byproduct of AGN feedback occurring in galaxies destined to become cluster members, both before and after cluster formation. Theoretical considerations suggest that the level of preheating ought to vary from one proto-cluster region to another. The entropy profiles of roughly 50% of the clusters with long central cooling times require that the gas be "preheated" to high entropy. Gas density profiles in such systems form hot central cores. Clusters with gas that isn't preheated to sufficiently high values forms peaked density profiles. I will show how variable preheating explain the various observed X-ray/X-ray correlations and discuss some of its implications for SZ studies. I will also present optical results that shed new light on the fate of the cold gas in cooling-unstable clusters, and propose observations tests of the "AGN preheating" aspect of the picture.

Neta Bahcall, Princeton

The Shape of Clusters and Large-Scale Structure

The largest structures in the Universe -- Superclusters of Galaxies -- range in size from a few Mpc to the 'Great Walls' scale of hundreds of Mpc. What is the shape of these large structures -- are they filamentary in nature or are they flattened two-dimensional 'pancakes'? How do they form and evolve? Superclusters are typically dominated by clusters of galaxies, systems that serve as one of the most powerful tools in cosmology. What is the shape of clusters -- are they spherically symmetric or are they elongated? Are they aligned with each other on large scales? I present results that answer these fundamental questions, revealing the predicted shape and evolution of the large-scale structure in the Universe in the current popular cosmology. We show that the shape of clusters provides an interesting new tool in constraining cosmology, as well as provides clues to the formation and evolution of large-scale structure.

Nick Battagalia, CITA

How non-thermal processes of the intracluster medium affect the Sunyaev-Zeldovich angular power spectrum

There is considerable uncertainty in the theoretical predictions for the angular power spectrum from the Sunyaev-Zeldovich effect (SZe). The level of precision reached by ACT, SPT, and Planck for measurements of the normalization of the SZe power spectrum, sigma_8, will be limited by the uncertainty in the theoretical models for the angular power spectrum. The uncertainties in the predicted spectrum arise from the complicated physics of the ICM. We have explored these ICM complexities using hydrodynamical simulations in a cosmological setting with several different variants of simulated physics, including cooling and star formation, star formation feedback by galactic winds and supernovae as well as cosmic ray physics.

Our statistics were compiled from two independently stacked cluster samples consisting of cosmological box simulations and individual high-resolution cluster simulations. We show that a simple parametrized fit describes averaged ICM pressure profiles sufficiently well and compare this finding to previous hydrostatic models. We find that radiative cooling and the associated star formation is the dominant physical process that modifies our fit parameters for these profiles and the angular power spectrum.

Brad Benson, University of Chicago

Studying Cluster Physics with SPT

Paul Bode, Princeton University

Energetics of the Intracluster Medium

Taking gravitational potential wells from a dark matter simulation, and assuming a polytropic equation of state and hydrostatic equilibrium, one can predict the state of the hot gas in clusters of galaxies. With reasonable values for star formation efficiency, energy input, and nonthermal pressure support, these model clusters can reproduce observed X-ray trends of gas temperature and gas mass fraction with cluster mass, as well as observed entropy and pressure profiles. Normalizing to X-ray observations is a vital step in using such models to predict the SZ signal.

Dick Bond, CITA

The Power of Sunyaev-Zeldovich, Then and Now

This talk will describe the theoretical history "THEN" of CITA's semi-analytic and simulation forecasts of the "ambient" (aka blank field) SZ effect, from the beginnings in the mid-80s to the "NOW" and near future of copious ACT and SPT ambient-SZ cluster detections, Along the way, we will recall the simulation and analytic state of SZ analysis of the CBI excess power in 2002 (and 2008) and the impact of ACBAR and BIMA on the results, now punctuated by recent QuAD and SZA releases, NOW the ACT, SPT and Planck pressure of high precision imminence in SZ is re-focussing us on pressure uncertainties in SZ power and maps from energy feedback, non-equilibrium and non-thermal processes, and cluster core complications as a function of redshift with large simulations. CITA's gassy-sim theoretical approach to this problem will be described, along with a conclusion that high resolution SZ and other observations must be our guide.

Tom Crawford, University of Chicago

A Real-World Example

Extracting compact sources from maps contaminated with noise and unwanted astrophysical signals is a well-studied problem. In anticipation of the now-current generation of large-scale SZ surveys, many authors arrived at the conclusion that a simple multi-scale spatial/spectral filter would be the optimal way to find galaxy clusters in data from these surveys. I will briefly present the basics of the spatial/spectral optimal filter and then show in some detail how this has been implemented in one real-world case, namely in data from the South Pole Telescope (SPT) survey.

Matt Dobbs, McGill University

The APEX Sunyaev Zel'dovich Experiment Observations

The APEX Sunyaev Zel'dovich experiment will be described and its performance since first light in 2006 summarized. Recent results will be presented together with plans for future observations/analysis.

Marian Douspis, IAS Orsay

Cosmological parameters from large and small scales CMB observations

Gus Evrard, University of Michigan, Ann Arbor

Recent Progress on Clusters at Michigan

The coming era of large, multi-wavelength surveys motivates and, ultimately, will inform a multivariate statistical framework describing cluster properties in relation to underlying halo mass and redshift. In this talk, I will present work at Michigan that focuses on a multivariate Gaussian likelihood approach to this problem, and includes empirical studies using optical and X-ray observations of the SDSS maxbcg sample as well as a computational program using Gadget resimulations of the Millennium Simulation with preheated gas dynamics. I will show evidence from the models that a combination of fgas measurements from X-rays along with Ytot from thermal SZ can constrain mass at the rms level of 4%.

Joe Fowler, Princeton University

Cluster survey with the Atacama Cosmology Telescope

In 2008, the Atacama Cosmology Telescope began its first full season observing a strip of the southern sky in three millimeter-wave bands. We present preliminary maps at 145 GHz featuring some SZ clusters.

The XMM Cluster Survey (XCS) is a serendipitous galaxy cluster survey being conducted using publicly available X-ray data from the XMM-Newton Science Archive. One of the primary aims of the XCS is to determine the form of the evolution of the cluster gas - knowledge of which is crucial for the use of X- ray or SZ selected clusters in constraining cosmological parameters - through measuring the X-ray scaling relations using a large, well characterised cluster sample spanning ~7 Gyr in lookback time. I will present an update on the status of the survey, discuss the expected cosmological constraints, and briefly describe some recent results from galaxy evolution studies conducted under the umbrella of the XCS project.

William Holzapfel, Berkeley

South Pole Telescope: A new probe of cluster cosmology

The South Pole Telescope (SPT) is a 10-meter diameter telescope with a 960 element millimeter-wavelength bolometric receiver, which is in the midst of its third season of observations at the South Pole. The SPT has been optimized for measurements of the Sunyaev-Zel'dovich (SZ) effect in galaxy clusters. With this instrument, we are surveying the southern sky to create a mass limited catalog of galaxy clusters out to the epoch of their formation. This program of observations will also produce significant detections of the kinetic SZ effect and weak gravitational lensing of the CMB, a multi-band millimeter-wavelength point source catalog, and images of the SZ effect in known galaxy clusters with unprecedented sensitivity. In this talk, I will discuss the design, construction, and deployment of the SPT telescope and receiver, progress of the observations, and conclude with a discussion of future plans.

Mike Jones, Oxford

Prospects for future SZ interferometers

Eiichiro Komatsu, University of Texas Austin

The Sunyaev-Zel'dovich effect as a probe of violent cluster mergers

In 2001 we made an unexpected discovery of a very bright SZ spot toward the X-ray luminous cluster RXJ1347-1145, which was significantly displaced from the center of the cluster's gravitational potential. One of the possible interpretations is that this spot is a signature of a violent merger in this cluster. This sypothesis has been confirmed by the subsequent Chandra X-ray observations. In this talk I will report on recent results from our follow-up observation of XJ1347-1145 with Suzaku X-ray telescope. Our studies show that the SZ effect, when it is mapped with a fine angular resolution of order 10 arc-seconds, provides a powerful probe of violent cluster mergers.

We build simple, 'top-down', models for the gas density and temperature profiles for clusters of galaxies based on current high precision XRay observations so as to 'exactly' satisfy observed XRay scaling relation between temperature and mass. The gas is assumed to be in hydrostatic equilibrium along with a component of non-thermal pressure due to dispersion and the gas fraction reaches universal value only at or beyond the virial radius. For these models, we calculate the Sunyaev-Zel'dovich Effect (SZE) scaling relations. We show that all the predicted SZE scaling relations between the integrated SZE flux and the gas temperature, the gas mass, the total mass, as well as, the gas fraction are in excellent agreement with recent SZE observations by Bonamente etal (2008). The consistency between the global properties of clusters detected in X-Ray's and in SZE hints that we are looking at the same population of clusters as a whole. Implications for SZE power spectrum, SZE flux-M200 scaling relation and number counts are discussed

Dan Marrone, University of Chicago

SZ Calibration with the Sunyaev-Zel'dovich Array

As observations of clusters through their SZ imprint on the CMB becomes more routine, it is now feasible to add this signal to the set of observables we use to study galaxy clusters. Using the Sunyaev-Zel'dovich Array (SZA), we are pursuing a variety of programs to investigate the correlation between cluster properties and their SZ signatures. I will present early results from these comparisons. The SZA is also a unique tool for resolved SZ imaging as part of the 23-element CARMA interferometer. I will discuss our initial experiment with heterogeneous array interferometry later this year and the future capabilities of the full array.

Brian Mason, NRAO

Mustang, the 90 GHz camera on GBT

Daisuke Nagai, Yale

Thermodynamics of Galaxy Clusters and Beyond

Clusters of galaxies are unique probes of cosmology and astrophysics, promising to provide new insights into both the nature of dark energy and dark matter and the physics of galaxy formation. One of the key challenges facing this approach lies in our understanding of cluster physics and their impact on cluster structure and evolution. In this talk, I will present numerical simulations of galaxy clusters and their comparisons to recent Chandra X-ray observations, with focus on thermodynamics of intracluster plasma. Numerical simulations including gas cooling and star formation reproduce global properties of the intracluster medium (ICM) and observable-mass relations with an accuracy of ~10%. I will further show that non-thermal processes, such as turbulence, cosmic-rays, and ICM plasma physics, will become important for understanding the remaining systematic uncertainty in the cluster mass estimate and cosmological constraints derived using galaxy clusters.

Christoph Pfrommer , CITA

The imprint of cluster physics on the Sunyaev-Zel’dovich effect -from bubbles to cosmological parameters

Clusters of galaxies provide us the opportunity to study an "ecosystem" - a volume that is a high-density microcosm of the rest of the Universe. At the same time clusters are excellent laboratories for studying plasma physical processes as well as for studying how super-massive black holes interact with the ambient cluster plasma. Guided by high-resolution simulations of galaxy clusters that self-consistently follow dissipative gas and cosmic ray physics, I will show how non-thermal processes in clusters build up over cosmic time. This enables us to understand how the Sunyaev-Zel'dovich effect and hydrostatic masses of galaxy clusters are expected to change - a finding which is critical in calibrating clusters as high-precision cosmological probes. On small scales, the Chandra X-ray Observatory is finding a large number of cavities in the X-ray emitting intra-cluster medium which often coincide with the lobes of the central radio galaxy. These are thought to provide the key for understanding the thermal evolution of galaxy clusters. I will argue that high-resolution observations of the Sunyaev-Zel'dovich effect are uniquely suited to unveil the composition of radio plasma bubbles. Solving this enigma would yield further insight into the complex physical processes within the cooling cores of clusters as well as provide hints about the composition of relativistic outflows of radio galaxies.

Peng Oh, University of California Santa Barbara

The imprint of supernovae and AGN feedback on the SZ sky

I discuss whether supernovae at high-redshift can result in a detectable SZ signal at small angular scales. I also discuss various aspects of AGN feedback on galaxy clusters.

Neelima Sehgal, KIPAC

Simulations of the Microwave Sky

New high-resolution, cosmological-scale simulations of the microwave sky have been created based on the most recent observational data. Currently these imulations are in use by the ACT team to test their data analysis pipeline. These simulations are also flexible enough to be of use to SPT and Planck. We discuss the various components of the simulations, their construction, and comparison to observational data.

Scaling relations among galaxy cluster observables, which will become available in large future samples of galaxy clusters, could be used to constrain not only cluster structure,but also cosmology. I will discuss the utility of this approach, employing a physically motivated parametric model to describe cluster structure, and applying it to the expected relation between the Sunyaev-Zel’dovich decrement (S_{\nu}) and the emission–weighted X–ray temperature (Tew). With a suitable choice of fiducial parameter values, the cluster model satisfies several existing observational constraints. A Fisher matrix is employed to estimate the joint errors on cosmological and cluster structure parameters from a measurement of S_{\nu} vs. Tew in a future survey. I will also compare the cosmology constraints from the scaling relation to those expected from the number counts (dN/dz) of the same clusters.

Laurie Shaw, McGill University

Characterizing the SPT cluster selection function

Sunyaev-Zel'dovich Effect (SZE) experiments such as the South Pole Telescope (SPT) are currently surveying a large area of sky searching for clusters via their imprint on the CMB. In order to use the resulting cluster catalogues for cosmology, it is necessary to know the mass- and redshift-dependent cluster selection function. I will describe ongoing work to understand and characterize the current SPT cluster yield, using synthetic SZ sky maps constructed from cosmological simulations and noise models calibrated against SPT data.

Jon Sievers, CITA

Cosmic Background Imager

Nicolas Taburet, IAS Orsay

The Sunyaev Zel'dovich contribution in CMB power spectra analysis : from contaminant to usefull signal

The Sunyaev Zel'dovich effect is expected to be one of the major contaminants at arcminutes scales in CMB analysis. I will present a method we developed at IAS to quantify the biases on parameter determination when any additive signal is not taken into account in the analysis. I will then present an application of this method in order to quantify the biases induced on cosmological parameter estimation when the SZ residuals are not properly taken into account in the analysis of the CMB. The important biases that would result from such a treatment encouraged us to developed a joint analysis of the CMB plus SZ signal that consists in determining the cosmological parameters fitting both signals. I will compare various methods to carry out such an analysis and will emphasize that only the coherent method that takes into account the dependency of the SZ spectrum with all the cosmological parameters allows an unbiased determination of the parameters. I will conclude by discussing the improvement on parameters error bars du to the extra information included in the SZ power spectrum and by pointing out the difficulties that our incomplete understanding of the intra cluster gas physics can set.

Howard Yee, University of Toronto

The Red-Sequence Cluster Survey and its Applications to Cosmology

The Red-Sequence Cluster Survey (RCS2) is a 1000-square-degree, multi-color imaging survey carried out using MegaCam on the 3.6m CFHT which is optimized for the search of galaxy clusters with 0.15<z<1.0 using the red-sequence method. Designed to create a well-characterized, large sample of clusters, the survey has the main goals of constraining cosmological parameters, studying galaxy cluster evolution, and discovering a large sample of strong gravitational lenses. I will give a summary of the current status of the RCS2 survey and discuss preliminary results on cosmological parameter fitting. I will present some Some initial results from an extension of the RCS method to Spitzer IRAC images from the SWIRE database to search for galaxy clusters in the "cluster desert" redshift range of 1<z<2 will also be shown.

Dennis Zaritsky, Stweard Observatory

The Stellar Components of Nearby Galaxy Clusters

A detailed understanding of galaxy clusters is essential in limiting the potential for systematic effects in the use of galaxy clusters for cosmological measurements. I will synthesize our current work on understanding the stellar components of galaxy clusters, including the intergalactic stellar populations and the structural relationship between stellar populations in galaxies and clusters. Ultimately, the characterization of the relationship between dark matter halos and the stellar populations within them will play a key role in unraveling what clusters tell us about the Universe.